1. Technical Field
The present invention relates to a yellow ink composition for inkjet recording having high color saturation, glossiness and light resistance, and to an inkjet recording method and inkjet recorded material using the yellow ink composition.
2. Description of the Related Art
Inkjet printers are widely used due to their advantages such as low acoustic noises and low running costs and printers capable of printing color images on plain paper are introduced into the market actively. However, it is extremely difficult to satisfy all the properties required of images produced using such printers, such as good color reproducibility, abrasion resistance, durability, light resistance, drying property, feathering, color bleeding, duplex printing, and ink discharging stability. As a result, ink is selected based on the particular application.
In general, the ink used inkjet recording is mainly composed of water, with a colorant and a wetter such as glycerin to prevent clogging. As the colorant, dyes are widely used for their coloring and stability. However, the light resistance and water resistance of images produced by using such dye-based ink are inferior. The water resistance can be improved in some degree by using specialized recording media having an ink absorbing layer, but is not satisfactory at all when it comes to plain paper.
To compensate for such defects, ink using a pigment has begun to be widely used as a colorant in recent years. Although the pigment ink is successful and superior to the dye ink with regard to light resistance, water resistance, etc., the coloring is degraded by coherence of light having difference wavelengths and phases produced by multiple reflection of light inside the pigment. Therefore, the pigment ink is inferior to the dye ink in general with regard to the coloring. In particular, the pigment ink used as ink for inkjet recording causes problems of deterioration of coloring (color saturation) on plain paper and gloss on specialized paper.
In an attempt to compensate for such degradation of coloring of the pigment ink, pigment particulates that are coated with resin are used. According to this method, the fixing property and the gas resistance property of the ink are further improved by the resin, and in addition dispersion is greatly stabilized. However, currently, pigment ink is not still on a par with dye ink with regard to gloss.
Japanese published unexamined application No. JP-2007-077340-A discloses an aqueous pigment dispersion comprising (A) an isoindoline-based pigment, (B) a pigment derivative obtained by introducing a sulfonic group into an isoindoline-based pigment, (C) water, and (D) a water-soluble organic solvent, characterized in that the ratio of the absorbance of the maximum peak among the peaks of an absorption spectrum in wavelengths of 400 to 800 nm to the absorbance of a valley nipped between peaks existing on the long wavelength side most near to the maximum peak is ≧1.29, which is excellent in dispersion stability and heat resistance. However, colorability and glossiness are not expected to improve. A ratio (Y/X) of an absorbance at 500 nm Y to the absorbance of the maximum peak X needs to be small to improve the colorability and glossiness. Therefore, this is different from the present invention.
The pigment ink has not had colorability and the glossiness better than that of a dye. A method of downsizing primary particles to improve the colorability is suggested. When the primary particles downsize, the absorbance of the maximum peak X at from 400 to 450 nm increases, and the ratio (Y/X) of an absorbance at 500 nm Y thereto decreases to improve the colorability.
However, only controlling the primary particle diameter of the pigment results in poor glossiness on gloss paper and coated papers.
Because of these reasons, a need exist for a yellow ink composition for inkjet recording, imparting colorability and glossiness to gloss papers and coated papers, and having high colorability on plain papers and preventing them from curling.